|  | 1.5 | Routing and the Different Classes of Routing Protocols
| 1.5.9 | Distance vector routing
Distance-vector routing protocols pass periodic copies of a routing table from router to router. Each router receives a routing table from its direct neighbor. For example, Router B receives information from Router A. Router B adds a distance-vector number (such as a number of hops), increases the distance vector, and then passes the routing table to its other neighbor, Router C. This same step-by-step process occurs in all directions between direct-neighbor routers. In this way, the protocol accumulates network distances so it can maintain a database of network topology information. Distance-vector protocols do not allow a router to know the exact topology of a network.